There are some R packages that allow for development of e-learning materials, these are Rmarkdown based so similar to knitr rather than sweave, but basically the same idea. The downside is the lack of symbolic support in R. Ximera does look interesting however. A second question I would have is how this would compare with Jupyter interactive notebooks which have LaTeX support and automated grading as well as symbolic algebra capabilities? Nevertheless additional tools are always welcome.